This invention relates to methods and apparatuses for controlling chemical interactions during planarization of microelectronic substrates, for example, controlling the interactions of a corrosion-inhibiting agent.
Mechanical and chemical-mechanical planarization processes (collectively xe2x80x9cCMPxe2x80x9d) are used in the manufacturing of electronic devices for forming a flat surface on semiconductor wafers, field emission displays and many other microelectronic-device substrate assemblies. CMP processes generally remove material from a substrate assembly to create a highly planar surface at a precise elevation in the layers of material on the substrate assembly. FIG. 1 schematically illustrates an existing web-format planarizing machine 10 for planarizing a substrate 12. The planarizing machine 10 has a support table 14 with a top-panel 16 at a workstation where an operative portion xe2x80x9cAxe2x80x9d of a planarizing pad 40 is positioned. The top-panel 16 is generally a rigid plate to provide a flat, solid surface to which a particular section of the planarizing pad 40 may be secured during planarization.
The planarizing machine 10 also has a plurality of rollers to guide, position and hold the planarizing pad 40 over the top-panel 16. The rollers include a supply roller 20, first and second idler rollers 21a and 21b, first and second guide rollers 22a and 22b, and take-up roller 23. The supply roller 20 carries an unused or pre-operative portion of the planarizing pad 40, and the take-up roller 23 carries a used or post-operative portion of the planarizing pad 40. Additionally, the first idler roller 21a and the first guide roller 22a stretch the planarizing pad 40 over the top-panel 16 to hold the planarizing pad 40 stationary during operation. A motor (not shown) drives at least one of the supply roller 20 and the take-up roller 23 to sequentially advance the planarizing pad 40 across the top-panel 16. Accordingly, clean pre-operative sections of the planarizing pad 40 may be quickly substituted for used sections to provide a consistent surface for planarizing and/or cleaning the substrate 12.
The web-format planarizing machine 10 also has a carrier assembly 30 that controls and protects the substrate 12 during planarization. The carrier assembly 30 generally has a substrate holder 32 to pick up, hold and release the substrate 12 at appropriate stages of the planarizing process. Several nozzles 33 attached to the substrate holder 32 dispense a planarizing solution 44 onto a planarizing surface 42 of the planarizing pad 40. The carrier assembly 30 also generally has a support gantry 34 carrying a drive assembly 35 that can translate along the gantry 34. The drive assembly 35 generally has an actuator 36, a drive shaft 37 coupled to the actuator 36, and an arm 38 projecting from the drive shaft 37. The arm 38 carries the substrate holder 32 via a terminal shaft 39 such that the drive assembly 35 orbits the substrate holder 32 about an axis Bxe2x80x94B (as indicated by arrow xe2x80x9cR1xe2x80x9d). The terminal shaft 39 may also rotate the substrate holder 32 about its central axis Cxe2x80x94C (as indicated by arrow xe2x80x9cR2xe2x80x9d).
The planarizing pad 40 and the planarizing solution 44 define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the substrate 12. The planarizing pad 40 used in the web-format planarizing machine 10 is typically a fixed-abrasive planarizing pad in which abrasive particles are fixedly bonded to a suspension material. In fixed-abrasive applications, the planarizing solution is a xe2x80x9cclean solutionxe2x80x9d without abrasive particles because the abrasive particles are fixedly distributed across the planarizing surface 42 of the planarizing pad 40. In other applications, the planarizing pad 40 may be a non-abrasive pad without abrasive particles. The planarizing solutions 44 used with the non-abrasive planarizing pads are typically CMP slurries with abrasive particles and chemicals to remove material from a substrate.
To planarize the substrate 12 with the planarizing machine 10, the carrier assembly 30 presses the substrate 12 against the planarizing surface 42 of the planarizing pad 40 in the presence of the planarizing solution 44. The drive assembly 35 then orbits the substrate holder 32 about the axis Bxe2x80x94B and optionally rotates the substrate holder 32 about the axis Cxe2x80x94C to translate the substrate 12 across the planarizing surface 42. As a result, the abrasive particles and/or the chemicals in the planarizing medium remove material from the surface of the substrate 12.
The CMP processes should consistently and accurately produce a uniformly planar surface on the substrate assembly to enable precise fabrication of circuits and photo-patterns. During the fabrication of transistors, contacts, interconnects and other features, many substrate assemblies develop large xe2x80x9cstep heightsxe2x80x9d that create a highly topographic surface across the substrate assembly. Yet, as the density of integrated circuits increases, it is necessary to have a planar substrate surface at several intermediate stages during substrate assembly processing because non-uniform substrate surfaces significantly increase the difficulty of forming sub-micron features. For example, it is difficult to accurately focus photo patterns to within tolerances approaching 0.1 micron on non-uniform substrate surfaces because sub-micron photolithographic equipment generally has a very limited depth of field. Thus, CMP processes are often used to transform a topographical substrate surface into a highly uniform, planar substrate surface.
In some conventional CMP processes, the planarizing pad 40 engages a metal portion of the substrate 12 having a highly topographical surface with high regions and low regions. The planarizing liquid 44 can include solvents or other agents that chemically oxidize and/or etch the metal to increase the removal rate of the metal during planarization. During the planarizing process, the beneficial accelerating effect of the etchant can be reduced because the etchant can act at least as quickly on the low regions of the metal portion as the high regions of the metal portion. Accordingly, the low regions may recede from the high regions and reduce the planarity of the substrate 12.
One approach addressing this potential drawback is to dispose a corrosion-inhibiting agent in the planarizing liquid 44 to restrict or halt the action of the etchant. This allows the mechanical interaction between the planarizing pad 40 and the substrate 12 to dominate the chemical interaction. Accordingly, the removal rate at the high regions of the microelectronic substrate 12 is generally higher than the low regions because the high regions have more mechanical contact with the planarizing pad 40 than do the low regions. As a result, the height differences between the high regions and the low regions are more quickly reduced. The inhibiting agent, however, can have adverse effects on the overall removal rate and other aspects of the planarizing process.
The present invention is directed toward methods and apparatuses for planarizing microelectronic substrates. A method in accordance with one aspect of the invention includes engaging the microelectronic substrate with a planarizing medium that includes a planarizing liquid and a planarizing pad having a planarizing surface and abrasive elements fixedly positioned at least proximate to the planarizing surface. The method further includes controlling an isoelectric point of at least a portion of the planarizing pad to be approximately equal to or less than a pH of the planarizing liquid, and moving at least one of the planarizing pad and the microelectronic substrate relative to the other to remove material from the microelectronic substrate.
In a further aspect of the invention, the isoelectric point of the planarizing pad can be controlled by controlling the isoelectric point of the abrasive elements in the planarizing pad. For example, the abrasive elements can be selected to include two constituents which, when combined, produce an abrasive element having the desired isoelectric point. Alternatively, different abrasive elements, each having a different isoelectric point, can be disposed in close proximity to each other in the planarizing pad to produce the desired aggregate isoelectric point.
In another aspect of the invention, the method can include engaging the microelectronic substrate with a planarizing medium that includes a planarizing pad having abrasive elements fixedly dispersed therein, and a planarizing liquid disposed on the planarizing pad. The planarizing liquid has a passivating agent, such as a corrosion-inhibiting agent. At least one of the planarizing pad and the microelectronic substrate is moved relative to the other to remove material from the microelectronic substrate. The method further includes controlling an amount of the passivating agent adsorbed to the abrasive elements by directing electromagnetic radiation toward the planarizing medium. The electromagnetic radiation can include ultraviolet radiation having a wavelength of from about 100 nanometers to about 350 nanometers, and the radiation can be directed toward the planarizing medium from a source spaced apart from the planarizing medium and/or from a carrier that supports the microelectronic substrate relative to the planarizing medium.
Another aspect of the invention is directed to an apparatus for removing material from a microelectronic substrate. In a further aspect of the invention, the apparatus can include a platen having a generally flat support surface, a planarizing pad supported on the platen and having a planarizing surface configured to support a planarizing liquid, and a carrier configured to engage a microelectronic substrate and support the microelectronic substrate adjacent to the planarizing pad, with at least one of the platen and the carrier being movable relative to the other. A plurality of abrasive elements are fixedly positioned in the planarizing pad at least proximate to the planarizing surface and have an aggregate isoelectric point selected to be less than a pH of the planarizing liquid. The abrasive elements can include a first constituent having a first isoelectric point and a second constituent having a second isoelectric point different than the first isoelectric point. For example, the second constituent can at least partially coat the first constituent. Alternatively, the abrasive elements can include first abrasive elements having a first isoelectric point and second abrasive elements having a second isoelectric point different than the first isoelectric point. The apparatus can still further include a source of high frequency electromagnetic radiation (such as ultraviolet radiation) directed toward the planarizing pad. The electromagnetic radiation source can be attached to the carrier or spaced apart from the planarizing medium.